FAQ · Sarking, anticon & reflective foil · SE Queensland
What is sarking / anticon / reflective foil for. Do I need it?
Sarking is a roof membrane; anticon is a thin under-roof blanket for noise and condensation. Neither replaces bulk ceiling insulation. The shiny reflective foil only works facing a clean air gap, and the Australian Government’s guide says dust and contact drop its value “towards zero.”
People ring me confused because a roofer mentioned sarking, an ad pushed “space blanket” foil, or a quote bundled in anticon, and they’re not sure if they’ve already paid for their insulation. So here’s the honest version of what each one is for, written by a bloke who pumps insulation for a living and still won’t sell you foil as the main event.
Three different things people lump together.
First, let’s sort out what these actually are, because they get lumped together and they shouldn’t be. Sarking is the membrane your roofer lays under the tiles or sheets. Its real job is keeping wind-driven rain, dust and embers out of the roof, and a vapour-permeable sarking also helps manage moisture. Anticon is a thin blanket of insulation bonded to a foil facing, rolled out under a metal roof mainly to cut the drumming of rain and to stop condensation dripping off the cold underside of the steel. Reflective foil(the shiny “space blanket” stuff) works by bouncing radiant heat back across an air gap.
Here’s the part that matters: none of those three is a substitute for a proper R-rated blanket of bulk insulation sitting on top of your ceiling. They’re roof-line products doing roof-line jobs: weather, noise, condensation. The layer that actually keeps the heat out of your rooms is the bulk insulation across the ceiling. So if a quote leaves you thinking the sarking or anticon “is” your insulation, that’s the misunderstanding to clear up first.
Reflective foil only works clean, and roofs aren’t clean.
I’m openly skeptical of reflective foil being sold as your main insulation, and the Australian Government’s own guide backs me up. Foil works by reflecting radiant heat back across a still air gap, so it only does anything when there’s a maintained air space next to the shiny surface. The yourhome.gov.au insulation guide says to maintain an air space of at least 25mm (45mm is ideal) next to the shiny surface, and that “contact with any other building element will reduce its insulative properties to zero.”
And then there’s dust. The same guide states plainly that “dust settling on the reflective surface of insulation greatly reduces its performance.” Up in a roof cavity, dust settles on horizontal foil within a season or two, so the R-value that looked good on the brochure quietly fades away. Bulk insulation like pumped cellulose doesn’t have that problem: it traps air inside the material itself, so it keeps doing its job whether it’s dusty, settled-on or sitting against a beam.
Already got anticon? Good. Now do the ceiling.
If you’ve got a metal roof with anticon already rolled out under it, that’s a good thing. It’s knocking down the rain noise and stopping condensation dripping off the underside of the sheet on a cold morning. I’m not knocking it for the job it’s doing. But it’s thin, it’s up at the roofline, and its foil only counts while it faces a clean air gap. It is not the same as a properly rated blanket sitting right on top of your ceiling, which is the layer that keeps the heat out of your rooms in a Queensland summer.
So the right way to think about it: anticon and sarking are part of the roof; bulk insulation is part of the house. You want both. We pump cellulose across the ceiling as one seamless blanket. Full contact across every inch, no gaps, and we let the anticon get on with the noise and condensation work it’s genuinely good at. I won’t tell you to rip the anticon out, and I won’t pretend it does the bulk-insulation job either.
“Foil is a bonus when it’s clean and has its air gap. It’s not the insulation. Get a proper R-rated blanket across the ceiling first; that’s the part that pays you back every summer.”
And because most people can never climb up to check any of this for themselves, it’s built into the system: every job is photographed and the photos are checked before you’re invoiced. The same on every job, run by Comfort Zone franchise owner-operators trained to one standard and held to it. So whatever’s already in your roof, you’ll see what we added and how it sits.
Sarking, anticon & foil: the related questions.
What is sarking / anticon / reflective foil for. Do I need it?+
Sarking is the membrane that sits under your roof to keep wind-driven rain and dust out; anticon is a thin blanket of insulation bonded to a foil facing, laid under a metal roof mainly to stop the drumming and the condensation drip. Neither is a substitute for proper bulk ceiling insulation. The shiny reflective foil on them only does anything when it faces a clean, still air gap of at least 25mm, and the Australian Government's yourhome guide says its value 'diminishes towards zero' once it gets dusty or touches another surface. In a roof, dust settles on it within a season or two. So if your roof already has sarking or anticon, good, but you still want a proper R-rated blanket across the ceiling. The foil is a bonus when it's clean; it's not the insulation.
Is reflective foil as good as bulk insulation?+
No, and the Australian Government's own guide is blunt about why. Reflective foil works by bouncing radiant heat back across a still air gap, so it only does anything when there's a maintained air space of at least 25mm next to the shiny surface (45mm is ideal). yourhome.gov.au states that contact with any other building element 'will reduce its insulative properties to zero', and that 'dust settling on the reflective surface of insulation greatly reduces its performance.' Up in a roof, dust settles on horizontal foil within a couple of seasons, so the number on the brochure quietly fades away. Bulk insulation, like pumped cellulose, works by trapping air in the material itself, so it keeps doing its job whether it's dusty or not. Foil has a place as part of a roof system, but it's not a replacement for a proper R-rated ceiling.
I've already got anticon under my metal roof. Do I still need ceiling insulation?+
Yes. Anticon does a real job. It's the thin foil-faced blanket your roofer rolls out under the steel to cut the rain noise and stop condensation dripping off the underside of the sheet on a cold morning. But it's thin, it's up at the roofline rather than across your ceiling, and its foil only counts while it faces a clean air gap. It is not the same as a properly rated insulation blanket sitting right on top of your ceiling, which is the layer that actually keeps the heat out of your rooms. Think of anticon as part of the roof and ceiling insulation as part of the house. You want both. We pump cellulose across the ceiling as one seamless blanket, full contact across every inch, and let the anticon get on with the noise and condensation job it's good at.
Why does reflective foil lose its R-value over time in a roof?+
Because the whole trick of reflective foil is a clean, shiny surface facing a still air gap, and a roof cavity destroys both of those over time. yourhome.gov.au lists 'dust settling on reflective insulation' as one of the things that reduces the total R-value, and notes that if foil isn't kept in continuous contact with an air gap its effective R-value 'diminishes towards zero' and condensation can form on the underside. Horizontal foil in a roof collects dust, and any spot where it touches a batten or a beam stops reflecting. So the foil number that looked good on the day can be most of the way gone a year or two later. That's exactly why I don't sell reflective foil as your main insulation, bulk cellulose doesn't care about dust; it just keeps trapping air and slowing the heat.
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